1. Field of the Invention
This invention relates broadly to pump sprayers preferably of the trigger-actuated hand-operated type. More particularly, this invention relates to the pressure build-up discharge assembly, and spring biased valve therefor, located at the fluid discharge nozzle end of such sprayers.
2. State of the Art
Many known pump sprayers have discharge valves at the nozzle end of the discharge passage for throttle valving the fluid pressure during pumping. The discharge valve forms part of an assembly including a spinner probe having spin mechanics of some type to effect a spinning or swirling action of the pressurized fluid to produce a spray discharge out of the orifice. Resilient means in the form of a separate coil spring or an integral plastic molded spring is provided for urging the valve onto its seat into a closed position. The valve opens in response to fluid pressure in the discharge passage which exceeds the closing force of the spring.
Such known sprayer discharge valves are typically of the throttling type, permitting the operator to control the actuation rate of the trigger sprayer, and such actuation rate determining the flow velocity. The flow velocity through the spin mechanics determines the size of the spray plume or more precisely the rotational velocity of the annular fluid sheet exiting from the orifice. The greater the velocity (the more energy in the spray plume) the thinner the annular sheet and the finer the particles created by breakup in the atmosphere. Thus the operator's pumping stroke rate varies the size and distribution range of the spray particles.
New product formulations require a narrow distribution range of particles and a predicted mean particle size. Thus, it was desirable to effectively regulate the operator's pumping stroke velocity and thereby produce a well-defined particle size and distribution range of fluid issuing from the discharge orifice as a fine mist spray.
Co-owned U.S. Pat. No. 5,522,547 to Dobbs, the teaching of which is hereby incorporated by reference herein, achieves this objective by the provision of a two-stage pressure build-up discharge valve assembly mounted at the end of the discharge nozzle surrounded by a nozzle cap. A high pressure throttle valve incorporating a valve and coil spring is coupled with a second stage low pressure sliding piston. The two stage valve member provides a predetermined pressure threshold which when exceeded by fluid pressure generated by the operator's finger force on the trigger actuator opens immediately permitting the fluid pressure to act upon the low pressure secondary piston abruptly snapping the valve assembly to a fully open flow position. At such position the operator's fingers are effectively caused to travel all or through most of the pump actuation stroke distance before the finger muscles can compensate and adjust to the lower force permitted by the second stage piston. However, when the finger muscles adjust to the lower actuation force and relax, the coil spring abruptly snaps the two-stage valve closed at a predetermined pressure.
At both the beginning of the pumping pressure stroke and at the end of pumping actuation, the two-stage valve snaps open and snaps closed immediately thereby eliminating the formation of large droplets at the beginning and at the end of each pressure stroke, thereby resulting in a uniform, repeatable mist spray.
While the discharge valve assembly described in Dobbs functions very well, the necessity of separate valve and coil spring in the assembly described therein increases the part count. It would be desirable to integrate the valve seat, spring and piston to reduce the number of components required for the assembly.
Several patents disclose a valve, compression spring and piston integrally molded for use in discharge valve assemblies. See, e.g., U.S. Pat. No. 4,153,203 to Tada, U.S. Pat. No. 4,273,290 to Quinn, U.S. Pat. No. 4,958,754 to Dennis, U.S. Pat. No. 4,989,790 to Martin et al., U.S. Pat. No. 5,234,166 to Foster et al., and U.S. Pat. No. 5,716,008 to Nottingham et al. However, such integrated components have disadvantages when used in the discharge valve assembly of the type described in Dobbs.
For example, it is desirable for the spring in a two-stage Doobs type discharge valve assembly to have a limited repeatable throw. Wave-shaped compression springs, which are common in integrated designs, are capable of a relatively large amount of compression. Further, it is desirable for the spring to be stably held within piston chamber in a manner which prevents spring buckling. Standard wave-shaped compression springs are subject to buckling. In addition, an integrated valve, spring and piston should be easy to manufacture. Double helix spring designs like that shown in U.S. Pat. No. 5,234,166 to Foster et al. are difficult to manufacture.